The number of operational mechanical cycles for a resistive potentiometer is limited by wear characteristics of a wiper moving over a resistive track. Many inventions have been patented to increase the lifetime of a potentiometer or variable resistor by reducing mechanical wear between the wiper and resistive track. U.S. Pat. No. 4,732,802 to Wayne P. Bosze, et. al. proposes to screen conductive islands onto a resistive track, allowing for reduced contact force, thereby extending life. The wiper may still come into contact with the material of the resistive track, thereby causing wear and/or the conductive islands may wear through. A similar technical approach is taught in U.S. Pat. No. 5,111,178, also by Bosze, whereby an admixture of conducting spheres and fibers are screened as integral components of the resistive track, and protruding above the resistive material. These additional components reduce wear directly on the resistive material, and reduce the required contact force. A similar idea is taught in U.S. Pat. No. 6,617,377 by Anthony Chacko. He suggests the use of nanocomposite compositions. The conductive material becomes a component of the resistive track material formulation and therefore limits the available materials for design of a resistive track.
Accordingly, it's desirable to invent a wear resistant surface that doesn't limit selection of a resistor material.
The most successful idea used in the vehicular industry to increase the lifetime of a potentiometer for a fuel level sender is taught in U.S. Pat. No. 4,931,764 by Robert Gaston. The invention is to place conductive bars or segments beneath a resistive track, said segments being connected by traces brought out in a planar or lateral direction away from the resistive material. A wiper rides on top of the displaced conductive segments or commutator bars. These commutator bars can be made from harder, longer-wearing material alloys and may have a lower coefficient of friction, resulting in a longer life for the potentiometer. But the lifetime is still not as long as desired. Also, the use of silver in commutator bars for fuel senders results in an adverse chemical reaction with fuel additives. Gold has been proposed as a replacement for silver in order to reduce undesirable chemical interactions. But, this adds cost to the product.
Accordingly, it's desirable to reduce the wear between a moving contact and a resistive or conductive track without using laterally displaced commutator bars. It's also desirable not to use precious metals or metals that may interact with a corrosive environment.
In order to reduce chemical interactions that may affect tracks or commutator bars containing silver, U.S. Pat. No. 6,681,628 B2 by Sawert, et. al. teaches a combination of two conductive ink printings, one of which is free from silver. The silver-free ink is printed directly over a resistive track containing silver. A wiper rides over this printed track, thus providing a harder and more chemically resistant wear-surface. However, the use of segmented bars described in the patent may result in wear of the resistive track as the wiper travels from bar to bar. If any part of this printing wears through, silver in the resistive track may become exposed to chemical effects.
U.S. Pat. No. 6,444,102 by Tucci teaches that a wiper made of carbon fibers can have a very long lifetime. A carbon fiber wiper is sold by Micro Contacts, Inc., 62 Alpha Plaza, Hicksville, N.Y. 11801-2695, and the company has tested a design with a durability of 500 million cycles while sliding on a surface. A resistive track cannot normally survive nearly as many cycles, and is therefore the basic limitation for designing a long life potentiometer or variable resistor.
Accordingly, a means for increasing the lifetime of a resistive track with a long lifetime wiper is desirable.
Another type of resistive potentiometer in current use today is a throttle position sensor (TPS) or a pedal position sensor (PPS). Both may have a wiper moving directly on a carbon based resistive track with no commutator bars. Even though these sensors have longer lifetimes than fuel level senders, even greater lifetimes with low wear and low electrical noise characteristics are desirable.
A moveable wiper used to select conductive patterns other than a resistive track is also desirable. A wiper with one or more prongs, said prongs isolated or in combination, may serve as a switching element, directly controlling current passing through selected parts of a conductive pattern. Multiple wiper prongs may select multiple contact conductors through the wiper movement and contact. In many of these cases, the highly conductive material may be soft and mechanical wear may limit the useful life of the conductor-wiper combination. An example of this kind of product is an absolute digital encoder that that may be used to measure and/or transmit angles for machine tool control and surveying equipment.
Accordingly, it's desirable to have a wiper-conductor system with long lifetime of wear for use with conductive tracks made of soft material.
Small D.C. motors have commutators and brushes (contact wipers) subject to severe mechanical wear. Separation of conductive areas for commutation is accomplished with air or insulating material gaps, redirecting coil current after a contact wiper passes into a new region. While the brush is in a commutator area relatively large with respect to the material thickness, the commutator is isotropically conductive. Although a commutator can be made with very high wear characteristics, wear is still a major problem for some applications.
Accordingly it is desirable to have a commutator and brush assembly with a very long life while using soft, highly conductive materials for current flow to the coils.
Yet another application is a very long lived contact switch whereby the wiper has some sliding motion during engagement with another component of the switch. Simple electrical contact switches may require millions of switch closures, and are therefore subject to wear. Versions of these switches may be used as cam-operated switches to control timing of operational cycles. The invented buffer allows very soft, highly conductive, materials on one side and hard, long-wearing materials on the contact side of these switches.
In all of these cases an improved wiper and contactor assembly with extended wear is desirable.